Thermoplastic articles



i atented Nov. 1 1 195 2 UNITED "STATES minimisesms'rm ARTICLES Raphael-Stern, So,uth River, N. J., assignor to Hercules Powder Company,Wilmington, Del,

a corporationlo'f .llelaware No -Drawing. Application November 30, 1 949I Serial No. 13%366" This invention relates t tou h. fir -r istant,dimensionallystable. mol d herm pl s a t cles. andmore particularly tosuch a t es fabricated from .celluloseacetate lcompqs tionsticizer fromthe plasticand very poor molding propertiesso that the molded objectsmadefrom Such la are d aded lnonhqm een qu 34 .9 exhibit unsatisfactoryphysical properties such as brittleness and poor dimensional stability.In order toovercome these disadvantages, it has been necessary to addsupplementary. plasticizers such as .dimethyl phthalate, .diethylphthalate and y eryl :triprop o ateawhi h are a iv s vents forthecellulose acetate but which do-not possess fire-resistant properties.These supplementary plasticizers must be incorporated in such high .coiCQntrationsa-s .to seriously impair or completelyfldestroy ,the fireresistance imparted by the phosphat plasticizers. Tributyl phosphate,although more compatible, .develops a putrid, obnoxious odor duringcompounding and molding which discourages its use. Consequently, moldedplastic articles fabricated-from prior art cellulose acetate plasticshave not been satisfactory with respect to a combination of toughness,fire resistance and dimensional stability.

Now in accordance with this invention, thermally shaped plastic articleshaving toughness equivalent to an Izod impact value of at least-1.5

foot-pounds per inch of notch, fireresistance defined asself-extinguishing, and dimensional stability equivalent to not morethan 4% loss in weight, and not more than i3% changef-inany dimension inaccordance with standard tests hereinafter set forth, are fabricatedfrom,com-- H t li ht-cit es. ellul s ace-tateand ;:plasticizer.watleash-2% .qfsa d through a hot :formingdie. to romp-elongatteams. (01. 106-:1???) p o p t r al r-bein'e resent in tri t ylphosphate. i

Plastic articles in accordance withthis invention exhibit excellenttoughness, fi e assi ta a d dimensional stability and re ain thesepropertiesoverextended pe iods Q l as ic ar icle 1i fi9dfi q wit thiinvention combine toughness and dimensional stability with fireresistance regardless of the fact that triethyl phosphate because of itsknown physical properties does not appear to be at all attractive as .aplasticizer for cellulose ester compositions --to be fabricated intothermal- 1y shaped plastic articles by injection, extrusion, for ',-c ompr.e.ssion molding methods. 'Iri- Tethyliphos phate .has a boiling pointof 216 C. and is theref ore generally considered to be too volatilefor'use in such plastics.

Furthermore, triethyl phosphate is soluble in water with decomposition.It .is, ltherefore, indeed surprising t t t ermally shapedp asti ar icle-con i i t y p s hateiin accor anc wit th invention ha e ex e e touhness and d mension ll abi ity, an r etai the ropertie O extendedperiods ofllse.

Havin described theinvention in a general way, the following examplesare given to illusratepec fic embodime t t e eon-hil thesefl not to .beconstrued as limiting the invention.

All parts in the following examples are parts by weight unless otherwiseindicated.

EXAMBLE I One hundred parts of --cellulose acetate PL-l, 25 parts oftriethyl phosphate, and 10 parts of triphenyl phosphate were premixedtogether in a [container in l'thle' absenqeo vola ile sol en :t form arelatively uniform dry premix. "This-dry premix was then colloided in aheated extrusion press, and-the colloided plastic mass was extruded rodswhich were cooled and' cutfinto molding powder granules. The resulting..moldin DQW was ,then injection molded into various Suitable moldcavities. to form lshapd .plastic', articles, in-

cluding various test pieces -such as bars, strips and discs.

.A specimenmolded in .the shape of .a bar 5 inches lorig, 4 /2-inqh;.iae, andi /2pi ch. thick, had an Izod impact valuefo'f 2.2 ifootepoundsper, inch of notch (1). Molded jstripsfi inches long, V inch wide, andA-inch-thick exhibited a fire reistanc d fin d J s n -extin ui in A sncime -mldedd ;the har 9 e i s? inches in diam ter an i/eri-nc 11 1 19.:w e d f (1) ASTM Test #D256-47T i (2) ASTM Test #D635-44 r (3) ASTMTest #D'756-46T, 3 cycles of procedure 1, followed by finalconditioning.

The ASTM tests for impact strength, fire resistance and dimensionalstability are standard, well-known tests and do not require detaileddescription here, since they are published in ASTM Standards onPlastics, September 1948, by the American Society for Testing Materials,1916 Race Street, Philadelphia 3, Pa.

Cellulose acetate PL-l utilized in Example I is a commercially availableproduct having a combined acetic acid content of 52-53.5% and aviscosity characteristic of less than 20 seconds, manufactured by theHercules Powder Company.

4 in a container with sufiicient acetonejao form a stiff paste. Thepaste was then rolled on a difierential two-roll mill with the rollsheated to 150-1'l0 F. to completely homogenize and colloid the mixture.Rolling was continued for approximately -40 minutes, after which themass formed a homogeneous, well-colloided, self-supporting sheet whichcould be stripped from the rolls, and a substantial portion of theacetone had been eliminated by evaporation. The plastic sheet wasstripped from the mill and was broken up into molding powder granules ina knife mill. The granules were spread in a thin layer on a tray andwere dried for approximately 24 hours in an air oven at C. The resultingdried molding powders were then injection molded into various suitablemold cavities to form shaped plastic articles, including various testpieces such as bars, strips and discs. The shaped plastic articles fromall of Examples V-XII, inclusive, possessed satisfactory toughnessequivalent to Izod impact values of at least 1.5 foot-pounds. per inchof notch, satisfactory fire resistance by being selfextinguishing, andsatisfactory dimensional stability equivalent to not more than 4% lossin weight, and not mor than :3% change in any dimension in accordancewith the standard ASTM tests set forth in Example I.

EXAMPLES II-IV Compositions in accordance with the formulations given inTable 1 below were prepared by the procedure given in Example Land theresulting molding powders were then injection molded into varioussuitable mold cavities to form shaped plastic articles, includingvarious test pieces such as. bars, strips and discs. Molded test piecessimilar to those used in Example I were tested in accordance with thestandard test procedures and the test data appear in Table 1.

Table 1 Cellulose acetate FM-G utilized in Examples V-XII, inclusive, isa commercially available product having a combined acetic acid contentof 55.5-56. and a viscosity characteristic of 35-55 seconds,manufactured by the Hercules Powder Company.

The thermally shaped plastic articles of this invention encompass anysuch article shaped or formed by any of the well-known molding processeswhich employ heat and pressure to shape and form them. For example, theshaped plastic Example No II Ingredients:

Cellulose Acetate PL-l Triethyl Phosphate Triphenyl Phosphate DimethylPhihalafe Test Date:

Izod Impg)ct(foot-poundspermch 3.5 2.7 3.7.

ofnotc Fire Resistance selflcxtinguishing. self-extinguishing"self-extinguishing. Dimensional Stability 2-inch disc,

%;-inch thick, percent change in: Weight 0.84 0.17 2.26. Diameter I-l.24 0.25 -0.80. -l.15. 0.45 1.40. Thickness +0.84 0.l6 -0.78.

Diameter II in the above table was at right angles to Diameter I.

The toughness, fire resistance and dimensional stability of the shapedarticles of Examples II, III, and IV were thus very satisfactory.

' 'EXAMPLES V-XII Compositions in accordance with the formulations givenin Table 2 below were prepared by mixing the ingredients of each formulatogether articles may be sheets, rods, tubes, etc. formed by extrudingthe thermoplastic compositions in accordance with this invention througha hot forming die. They may be innumerable objects such as motorhousings, electrically lighted ornaments, household articles,"tjoiletryarticles, toys, etc. formed by injection molding the thermoplasticcompositions in accordance with this invenally spa-sea treats; articlesor "this tron are "when, fire resistant andfd'ihi'nsessfjalloffthesef'attr'ibutes 'ih ed arid "defih d by "the Q"The property of toughness contemplated by thisir'i' tionds thesi'st'ance pff'theshaj'ped plasticarticl'esto b b a'rpimpact 'flh'e Izodimpact stre pr'eiiertypr it p lent to Izod ,impa'c I pounds per of Itchas standardnsTMtest for mpact in Exampl'efI. ,Furthjernio're,

The "shaped plastic articls of this invention are fire resistant to adegree "defined as selfextinguishing. This 1 means jthat thef'articl'es,

*hehgsiibjectd to adiier se conditions of heat' andnio'i'sture'eXposure. In accordanc'e vviththis invntion,thexshapedplastic' articles will show not more -tha'n' l loss in 'weight, and notmore than 13%;" change :in any dimension in accordance with:theistandard 'ASTM test for; resistance :of jplastics to acceleratedservice conditions set forth xam e-L The; pla ic a c s. f this inventionretain: this measure oPdimensional stability ver ex ds 'p tiodsz 1 V Byany dimension is meant any dimension capable-of beingaccuratelymeasured, such as thickness, width, length, height, depth, diameter,inside diameter, outside diameter, etc. The dimensions selected formeasurement will depend somewhaton the shape and "configuration'of theparticular article being measurd.""For example, the dimensions of asolid rod include diameter, circumference and'length. The dimensions ofa uie flimi'ts defined, it ha been found that ether measurabl dimensionsare Iikewi's'e stab1e within thelimitsdefine by this "invention.

A thermoplastic "cellulose acetate nec ssary componentof the thermally"shaped fplasti'c articles "of this 'invention. Suitable celluloseacetates "will ihave a substitution equivalent to between about 52%fandj about combined acetic 'acidand aviseosity'chara'cteristiclessthanabout 600 seconds. Cellulose acetates having *a substitution equivalentto between "about 52% and 57% combined acetic acid and a viscositycharacteris'ticbelow about 100 seconds "arepreferred, howeye'r. p

The amount meanness-ac tate "employedwill Vary Within "relatives wide"limits, depending upon the 'arti'cl'efmo'lding characteristics, plasticnow; and hardness desired. Usually the amount of celluloseacet'ateutilizedwill be betweenabout 60%and8 4. 5%byweightofthecombiried weight of the "cellulose acetate and plasticize'rcomponents of "the plastic articles of this invention. Within the "broadrange" of operability, th'e fprefer'red an ount'employed will -bebetween about and by weight oi-"the combined weight of cellulose"acetate and -plasticizercomponents of the'articles. p

I A major or substantial proportion amounting to'at least'about 65% byweight, and preferably all,of the plasticizer-component-of the plasticarticles of this-invention must be organic-phosphoric acidesteroffthegroup consistingof trij ethyl phosphate and mixtures oftriethyl {phosphate with at lQa'Stone other organic phosphoric acidester.

Sufii'cientf organic phosphoric acid ester of thegroup set forth mustbe-present so "that the articles of this-invention contain'at least 6.5%phosphate radical based on the-combined weight of the cellulose'esterand plasticizer components of the articles, 'and*preferab1y 8;0 'ormore.

'Triethyl phosphate is f a necessary component in accordance "with thisiriventionfand must-be present in eacharticle in sufiicient quantity tosupply at least 20% of the phosphate radical present in thearticle,Moreovergtriethyl phos- 'phate alone isan excellent solvent plasticizerfor "thethermoplastic lower organic esters 0f cellulose, and can beemployed as the sole pla'sticizing agent, as illustrated in Examplev.Itis'prferable, however, to employ a mixture "of -triethyl phosphatewith at least one other brg'anic phosphoric acid ester,"because bysocornea -much greater freedomof formulation is made-possible in order mymeet desired p'lastic flow, hardness,

molding'conditions, etc. Any' organic phosphoric acid estefi'ri'ay bemixed" with'the trithyl'phosphate. Suitable esters-include '-tripropyl--phos- "phate, tributylfphosphate," tri'amyl phosphate,

trihekyl phosphate, trioctyl phosphate, triphenyl phate, Qnethyl'diph'enyl phosphate, f ethyl oliph'nyl phosphate," fbutyl diphenylphosphate, cresyl"diphenylphosphate;"etc, 'The'proportions of "triethyl"phosphate? and other organic 1- phosphoric acid -ster"within' suchmixtures may "be variedwithin "wide liriiitsto obtain a suitableplasticfiow, hardness, molding characteristics,

etc., the only limitations}being with] respect Ito the "total' phosphateradical which imist be present and the amount of this radical which must"be supplied by triethyl phosphate. Withm the broad operable range,preferred mixtures comprise between about 10% and 25% by weight oftriethyl phosphate and between about and 25% by weight of triphenylphosphate, based on the combined weight of the cellulose acetate andphosphoric plasticizers. It has been further iound that when theproportion of triethyl phosphate is between about and about 25% byweight and the proportion of triphenyl phosphate is between about 5% andabout based onthe combined weight of the cellulose acetate andphosphoric plasticizer, the shaped plastic articles of this inventionare remarkably resistant to plasticizer exudation under adverseconditions of exposure. For example, shaped articles formulated withinthese limits for the triethyl phosphate and triphenyl phosphatecomponents do not exude plasticizer even after 60 hours of exposure at140 F. and 88% relative humidity.

A minor proportion amounting to not more than about 35% by weight of thetotal plasticizer componentof the articles of this invention may besupplemental plasticizers such as dimethyl phthalate, diethyl phthalate,methylphthalyl ethyl glycolate, glyceryl tripropionate, etc. Suchplasticizers, although excellent solvents for cellulose acetate must beutilized in limited qauntities, as defined, in order not tosubstantially impair the fire resistance of the shaped plastic articlesof this invention. Preferably the supplemental plasticizer shouldconstitute not more than about by weight of the total plasticizercomponent.

The plastic articles of this invention may contain various auxiliarycomponents such as pigments, dyes, fillers, lubricants, waxes, etc.,usually in minor amounts, to impart desired properties such as color,waterproofness, easy mold release, etc.

Other methods of compounding well known in the plastics art may beemployed'instead of the hot extrusion method employed in Examples I-IV,and the solvent process employed in Examples V-XII. For example, thecellulose acetate and plasticizer components together with auxiliarymaterials may be mixed and colloided on a hot two-roll mill or in a hotBanbury mill in the absence of volatile solvent and the resultingcolloided mass shaped by subsequent hot molding operations.

Since the plastic articles of this invention are characterized by beingtough, dimensionally stable and self-extinguishing, they are thereforeparticularly suitable for many industrial, home and personal uses. Theyare especially suitable for uses where industrial, insurance or safetyrequirements make it necessary or desirable to employ plastic articleswhich are self-extinguishing and will not propagate a fire, and whichadditionally must be tough and dimensionally stable in order tosuccessfully perform their useful function. Typical uses include suchthings as various electrical appliances including motor housings,electrically lighted Christmas tree ornaments, vacuum cleaner housings,electrically driven tool handles, electrically powered deodorantdispensers, toiletry articles, toys, etc.

The viscosity characteristic of the cellulose acetate materials of thisinvention expresses the time of fall of a %-inch steel ball through 10inches of a 20% solution (by weight) of the cellulose acetate dissolvedin a solvent composed of 90:10 acetone ethyl alcohol (by weight),confined in a 1-inch inside diameter glass tube, at 25 C.

What I claim and desire I to protect by Letters Patent is:

1. Thermally shaped plastic articles comprising between about 60% and84.5% of thermoplastic cellulose acetate and between about 40% and 35.5%of plasticizer, each based on the combined weight of cellulose acetateand plasticizer, at least 65% of said plasticizer consisting of amixture of triethyl phosphate and at least one triaryl phosphoricacidester, said triaryl phosphoric acid ester constituting at least 5% ofthe combined weight of cellulose acetate and plasticizer, the mixture ofphosphate plasticizers being proportioned so that the shaped plasticarticles contain at least 6.5% by weight of phosphate radical based onthe combined weight of cellulose acetate and plasticizer, at least 20%of said phosphate radical being present in said triethyl phosphate, saidarticles characterized by toughness equivalent to an Izod impact valueof at least 1.5 footpounds per inch of notch, fire resistance defined asself-extinguishing, and dimensional stability equivalent to not morethan 4% loss in weight, and not more than 13% change in any dimens1on.

2. Thermally shaped plastic articles in accordance with claim 1 in whichthe triaryl phosphoric acid ester is triphenyl phosphate.

3. Thermally shaped plastic articles in accordance with claim 1 in whichthe triaryl phosphoric acid ester is tricresyl phosphate.

4. Thermally shaped plastic articles in accordance with claim 1 in whichthe triaryl phosphoric acid ester is cresyl diphenyl phosphate.

5. Thermally shaped plastic articles comprising between about 65-80%cellulose acetate having a combined acetic acid content between about52% and 57% and a viscosity characteristic of less than about seconds,10-25% triethyl phosphate, and 5-25% triphenyl phosphate; said articlescharacterized by toughness equivalent to an Izod impact value of atleast 1.5 foot-pounds per inch of notch, fire resistance defined asself-extinguishing, and dimensional stability equivalent to not morethan 4% loss in weight, and not more than 13% change in any dimension.

6. Thermally shaped plastic arcticles comprising between about 65-80%cellulose acetate having a combined acetic acid content between about52% and 57% and a viscosity characteristic of less than about 100seconds, 1025% triethyl phosphate, and 5-15% triphenyl phosphate; saidarticles characterized by toughness equivalent to an Izodimpact value ofat least 1.5 footpoun'cis per inch of notch, fire resistance defined asself -extinguishing, dimensional stability equivalent to not more than4% loss in weight, and not more than :3% change in any dimension, andfreedom from plasticizer exudation after 60 hours of exposure at F. and88% relative humidity.

RAPHAEL L. STERN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,981,132 Walsh Nov. 20, 19342,021,901 Smith Nov. 26, 1935 2,328,269 Gloor Aug. 31, 1943 OTHERREFERENCES Handbook Plastics-Simmonds et al.-1943 s. 260, 261, 270and'2'71. pg

1. THERMALLY SHAPED PLASTIC ARTICLES COMPRISING BETWEEN ABOUT 60% AND84.5% OF THERMOPLASTIC CELLULOSE ACETATE AND BETWEEN ABOUT 40% AND 15.5%OF PLASTICIZER, EACH BASED ON THE COMBINED WEIGHT OF CELLULOSE ACETATEAND PLASTICIZER, AT LEAST 65% OF SAID PLASTICIZER CONSISTING OF AMIXTURE OF TRIETHYL PHOSPHATE AND AT LEAST ONE TRIARYL PHOSPHORIC ACIDESTER, SAID TRIARYL PHOSPHORIC ACID ESTER CONSTITUTING AT LEAST 5% OFTHE COMBINED WEIGHT OF CELLULOSE ACETATE AND PLASTICIZER, THE MIXTURE OFPHOSPHATE PLASTICIZERS BEING PROPORTIONED SO THAT THE SHAPED PLASTICARTICLES CONTAIN AT LEAST 6.5% BY WEIGHT OF PHOSPHATE RADICAL BASED ONTHE COMBINED WEIGHT OF CELLULOSE ACETATE AND PLASTICIZER, AT LEAST 20%OF SAID PHOSPHATE RADICAL BEING PRESENT IN SAID TRIETHYL PHOSPHATE, SAIDARTICLES CHARACTERIZED BY TOUGHNESS EQUIVALENT TO AN IZOD IMPACT VALUEOF AT LEAST 1.5 FOOTPOUNDS PER INCH OF NOTCH, FIRE RESISTANCE DEFINED ASSELF-EXTINGUISHING, AND DIMENSIONAL STABILITY EQUIVALENT TO NOT MORETHAN 4% LOSS IN WEIGHT, AND NOT MORE THAN $3% CHANGE IN ANY DIMENSION.